Firstly, Schneider and Rasool isn't. Getting them the wrong way round is always a bit of a tell-tale of a cp from a sketpic source. Its Rasool and Schneider; more here: www.wmconnolley.org.uk/sci/iceage/

"Crazy" LH said: R+S said: "It is found that, although the addition of carbon dioxide in the atmosphere does increase the surface temperature, the rate of temperature increase diminishes with increasing carbon dioxide in the atmosphere." So Ender, Phil, and whoever, this clearly shows that as CO2 keeps increasing, the surface temperature actually starts decellerating. Do any of you actually read and think about what you have read? Then increased CO2 causes cooling.

LH is wrong (well of course he is, he's wrong about everything!). Increasing CO2 increases T roughly logarithmically. This is well known, and its what S is saying. But adding CO2 always causes warming in those models.

All this Hockey Stick stuff is just not as important as people seem to think it is - it wasn't central to the TAR; thats just septics puffing it for reasons of their own. And it has little to do with attribution of current changes. See The Big Picture

Was the MWP global? Castles doesn't seem to have read the TAR: the relevant bit is http://www.grida.no/climate/ipcc_tar/wg1/070.htm, to quote "As with the “Little Ice Age”, the posited “Medieval Warm Period” appears to have been less distinct, more moderate in amplitude, and somewhat different in timing at the hemispheric scale than is typically inferred for the conventionally-defined European epoch. The Northern Hemisphere mean temperature estimates of Jones et al. (1998), Mann et al. (1999), and Crowley and Lowery (2000) show temperatures from the 11th to 14th centuries to be about 0.2°C warmer than those from the 15th to 19th centuries, but rather below mid-20th century temperatures. The long-term hemispheric trend is best described as a modest and irregular cooling from AD 1000 to around 1850 to 1900, followed by an abrupt 20th century warming..." and so on. M.K. Hughes and H.F. Diaz, "Was there a 'Medieval Warm Period?", Climatic Change 26: 109-142, March 1994 is worth a read.

Castles quotes "Finally, on the realclimate site William Connelley [sic] says that it's about time that Castles and Henderson got off their bums and produced their own scenarios!". Yes indeed. In fact even people like Tol admit that using your assumptions makes essentially no difference to the end product.